Live map shows the air-pollution level in hundreds of cities around the world

We've long known that air pollution is associated with health problems like respiratory disease and lung cancer, and a recent study published in the journal Nature tried to quantify its full human toll. Air pollution, the authors concluded, contributes to approximately 3.3 million premature deaths worldwide each year.

The study's authors noted that it was difficult to gather data for the research because so many places didn't keep track of air quality. The World Air Quality Index is trying to change that with a map that tracks air-quality measurements in cities around the world in real time.

Areas that are green have good air quality, while dark-red areas have dangerous air quality that could be hazardous to health.

http://waqi.info/

The project pulls information from about 8,000 government air-quality measurement stations. The map is not complete, though — it includes only about 1,000 cities, and much of Africa, South America, and the Middle East are blank. Still, it's a good start and a good resource to identify the areas that need the most attention.

The map uses the same air-quality index as the US Environmental Protection Agency. Anything below a 100 AQI (yellow), is considered safe, according to the EPA.